Selective adsorption of anions on hydrotalcite-like compounds derived from drinking water treatment residuals.

Most drinking water treatment residuals (DWTRs) with rich metal resources are landfilled directly without treatment, which results in wasted Al/Fe resources. This work proposes a new method of preparing Mg-Al-Fe Hydrotalcite-like compounds (MAF-HTCLs) by recycling DWTRs as the raw material to selectively adsorb anions in the waste water. In this study, MAF-HTCLs were prepared by the coprecipitation method with recycled DWTRs. The characterizations and adsorption of MAF-HTCLs were studied for the selective adsorption of P, Cr, F, and Br. The adsorption capacity was increasing as the value of pH decreased. For kinetic adsorption, the pseudo-second-order model fit better, and two isotherm models (the Langmuir and Freundlich models) described the isotherm results well. According to the Langmuir model, the maximum adsorption capacities of P, Cr, F, and Br were 55.2, 34.9, 16.84, and 13.9 mg/g, respectively. Based on the results of characterizations before and after adsorption, adsorption mechanisms of Cr, F, and Br were proposed, including physicochemical adsorption, surface complexation, and ion exchange, in which ion exchange was dominant. Finally, we determined that the selective adsorption mechanisms of P on MAF-HTCLs included strong ion exchange and surface chemical precipitation by analyzing the results of X-ray photoelectron spectroscopy.